1. Field of the Invention
This invention relates generally to determining analyte concentrations within living tissue. More particularly, this invention relates to a device for isolating regions of living tissue for consistent transfer of thermal spectra to and from the tissue.
2. Description of the Related Art
Millions of diabetics are forced to draw blood on a daily basis to determine their blood glucose levels. A search for a non-invasive methodology to accurately determine blood glucose levels has been substantially expanded in order to alleviate the discomfort of these individuals. A significant advance in the state of the art of non-invasive blood glucose analysis has been realized by an apparatus taught in U.S. Pat. No. 6,198,949, titled SOLID-STATE NON-INVASIVE INFRARED ABSORPTION SPECTROMETER FOR THE GENERATION AND CAPTURE OF THERMAL GRADIENT SPECTRA FROM LIVING TISSUE, issued Mar. 6, 2001, and by methodology taught in U.S. Pat. No. 6,161,028, titled METHOD FOR DETERMINING ANALYTE CONCENTRATION USING PERIODIC TEMPERATURE MODULATION AND PHASE DETECTION, issued Dec. 12, 2000, both of which are hereby incorporated in their entirety by reference.
U.S. Pat. No. 6,198,949 discloses a spectrometer for non-invasive transfer of thermal gradient spectra to and from living tissue. The spectrometer includes an infrared transmissive thermal mass, referred to as a thermal mass window, for inducing a transient temperature gradient in the tissue by means of conductive heat transfer with the tissue, and a cooling system in operative combination with the thermal mass for the cooling thereof. Also provided is an infrared sensor for detecting infrared emissions from the tissue as the transient temperature gradient progresses into the tissue, and for providing output signals proportional to the detected infrared emissions. A data capture system is provided for sampling the output signals received from the infrared sensor as the transient temperature gradient progresses into to the tissue. The transient thermal gradients arising due to the intermittent heating and cooling of the patient""s skin generate thermal spectra which yield very good measurements of the patient""s blood glucose levels.
Although the apparatus taught in the above-mentioned U.S. Pat. No. 6,198,949 has led to a significant advance in the state of the art of non-invasive blood glucose analysis, one possible source of error arises due to the nature of the contact between the thermal mass window and the patient""s skin. If several separate measurements are required, it follows that the thermal mass window must be brought into contact with the patient""s skin several times. The problem with this is that each of such contacts tends to be slightly different. For instance, slight differences in skin topology and/or pressure may arise at the interface between the thermal mass window and the skin; the patient may move that portion of his or her body, for instance the arm, which is in contact with the thermal mass window; and muscular tension may change between measurements. Each of these factors, and perhaps others as well, tend to complicate the already complex nature of the contact between the skin and the thermal mass window.
A device and method are provided for use with a non-invasive optical measurement system, such as but not limited to a thermal gradient spectrometer for improved determination of analyte concentrations within living tissue. In a preferred embodiment, a site selector is secured to a patient""s forearm thereby isolating a measurement site on the patient""s skin for determination of blood glucose levels. The site selector attaches to or engages a window of the gradient spectrometer and thus forms an interface between the patient""s skin and the window. When the spectrometer must be temporarily removed from contact with the patient""s skin, such as to allow the patient mobility, the site selector is left secured to the forearm so as to maintain a consistent measurement site on the skin. When the spectrometer is later reattached to the patient, the site selector will again form an interface between the spectrometer and the same location of skin as before.
In one embodiment, a device for use with a non-invasive optical measurement system comprises a generally flat member having an aperture passing from a first surface of the flat member to a second surface of the flat member. The flat member is preferably made of injection-molded plastic, and may be configured to minimize the formation of condensation thereon. The aperture has a predetermined cross-sectional shape and allows substantially unimpeded transmission of thermal spectra to and from skin of a patient through the flat member. The first surface comprises a contact surface which presses against the skin of the patient when the flat member is attached thereto. The second surface comprises an interface surface which is shaped to receive the non-invasive optical measurement system.
A fastening strap may be connected to the flat member and adapted to attach the flat member to a predetermined location on the patient, such as a forearm. The fastening strap comprises a fixed end and an adjustable end. The fixed end passes through a first of opening within the flat member and the adjustable end passes through a second of opening within the flat member such that the fastening strap assumes an annular configuration having an interior surface and an exterior surface. The fixed end is folded back and affixed to the interior surface of the fastening strap, and the adjustable end is folded over and removably attached to the exterior surface of the fastening strap with a fastener such as a buckle or Velcro(trademark).
In another embodiment, the contact surface of the flat member includes adhesive material which is adapted to attach the flat member to the predetermined location on the patient. With this embodiment, the contact surface includes a pressure sensitive adhesive surface which enables attaching the site selector to the patient""s skin without using the above-mentioned fastening strap.
In operation the flat member and the aperture cooperate to grip the skin of the patient when pressed against the skin under force applied by the fastening strap. Furthermore, the flat member is coupled with the non-invasive optical measurement system such that removal of the measurement system from the flat member leaves the predetermined location on the patient substantially unaltered.
One aspect of the invention provides a device for maintaining a predetermined location on the skin of a patient to facilitate use of a noninvasive optical measurement system. The device comprises a generally flat member having an aperture passing from a first surface of the flat member to a second surface of the flat member. Preferably, the flat member is made of a rigid material, such as injection-molded plastic. The aperture is adapted to allow substantially unimpeded transmission of thermal spectra to and from skin of a patient through the flat member. The first surface comprises a contact surface which presses against the skin of the patient when the flat member is attached thereto. The second surface comprises an interface surface which is shaped to receive the noninvasive optical measurement system. The interface surface preferably comprises at least one raised section which facilitates orienting the noninvasive optical measurement system relative to the flat member such that the noninvasive optical measurement system assumes angular and axial alignment with the aperture. The aperture preferably comprises at least one protrusion which facilitates attaching the noninvasive optical measurement system to the flat member such that the interface surface receives the noninvasive optical measurement system. The flat member and the aperture cooperate to grip the skin of the patient when applied to the skin.
A fastening strap is connected to the flat member and is adapted to attach the flat member to the predetermined location on the skin of the patient. The fastening strap comprises a fixed end and an adjustable end. The fixed end passes through a first opening within the flat member and the adjustable end passes through a second opening within the flat member such that the fastening strap assumes an annular configuration having an interior surface and an exterior surface. The fixed end is folded back and affixed to the interior surface of the fastening strap, and the adjustable end is folded over and removably attached to the exterior surface of the fastening strap.
Another aspect of the invention provides a method for consistently isolating regions of living tissue for transfer of thermal spectra between the tissue and a noninvasive optical measurement system. The method comprises attaching a site selector to a predetermined region of skin on a patient. The site selector comprises a generally flat member having an aperture passing from a first surface to a second surface of the flat member. The first surface comprises a contact surface which presses against the skin of the patient when the flat member is attached thereto, and the second surface comprises an interface surface which is adapted to receive the noninvasive optical measurement system. The aperture is adapted to allow substantially unimpeded transmission of thermal spectra through the flat member between the contact surface and the interface surface. Pressure between the site selector and the patient""s skin causes the perimeter of the aperture to enter into a gripping relationship with the skin, thereby minimizing relative motion between the site selector and the skin. This gripping relationship provides location stability whereby the site selector is prevented from sliding across the skin when the site selector is pushed or otherwise acted on by an external force.
The method further comprises placing the noninvasive optical measurement system in intimate contact with the interface surface of the site selector. A window of the noninvasive optical measurement system interfaces with the aperture and is placed in thermal contact with the predetermined region of skin on the patient. The noninvasive optical measurement system is removably attachable to the site selector such that the noninvasive optical measurement system may be attached to and detached from the site selector while the site selector remains attached to the skin of the patient such that a consistent measurement site on the skin is maintained.
Another aspect of the invention provides a device for consistent placement of a predetermined region of a patient""s skin against an analysis window of a noninvasive optical measurement system. The device comprises a contact surface of the noninvasive optical measurement system, which comprises the analysis window, a first alignment window, and a second alignment window, a first alignment mark printed on the patient, and a second alignment mark printed on the patient. Alignment of the first and second alignment windows respectively with the first and second alignment marks causes the predetermined region to align with the analysis window. Preferably, the first and second alignment windows each provides optical access to skin of the patient, and thus enables visual navigation of the noninvasive optical measurement system on the skin.
Still another aspect of the invention provides a method of consistently isolating regions of living tissue for transfer of thermal spectra between the tissue and a noninvasive optical measurement system. The method comprises applying a first alignment mark and a second alignment mark to a region of skin on a patient such that when the first alignment mark is coincident with a first alignment detector of the noninvasive optical measurement system and the second alignment mark is coincident with a second alignment detector of the noninvasive optical measurement system, an analysis window of the noninvasive optical measurement system is caused to be centered and aligned with a predetermined location on the skin. The method further comprises placing the window of the noninvasive optical measurement system in thermal contact with the predetermined location on the skin, and moving the skin and/or the noninvasive optical measurement system relatively until the first and second alignment detectors are centered and aligned respectively with the first and second alignment marks.
In another aspect of the invention, a device is provided for consistently isolating regions of living tissue for transfer of thermal spectra between the tissue and a noninvasive optical measurement system. The device comprises a site selector comprising a generally flat member having an aperture passing from a first surface of the flat member to a second surface of the flat member. Preferably, the flat member is made of injection-molded plastic comprising a material which minimizes a formation of condensation thereon. The aperture is adapted to allow substantially unimpeded transfer of thermal spectra through the flat member. The first surface comprises a contact surface which presses against the skin of the patient when the flat member is attached thereto. The aperture grips the skin of the patient when the site selector is pressed thereon such that relative motion between the site selector and the skin is minimized. The second surface comprises an interface surface which is shaped to receive the noninvasive optical measurement system.
The device further comprises an alignment marker printed onto the skin of the patient. Aligning the aperture with the alignment mark facilitates orienting the site selector relative to a predetermined location on the patient such that when the noninvasive optical measurement system is coupled with the site selector, the noninvasive optical measurement system is centered and aligned with the predetermined location on the patient.
In still another aspect of the invention, a method is provided for consistently positioning a predetermined region of a patient""s skin against a window of a noninvasive optical measurement system. The method comprises applying an alignment mark to the skin of the patient, aligning a site selection member with the alignment mark and securing the site selection member with respect to the skin of the patient, and coupling the noninvasive optical measurement system to the site selection member, thereby bringing the window of the noninvasive optical measurement system into thermal contact with the predetermined region on the patient. The site selection member preferably comprises a flat member having an aperture passing from a first surface of the flat member to a second surface of the flat member. The aperture allows substantially unimpeded transmission of thermal spectra to and from the skin of the patient through the flat member. The first surface comprises a contact surface which presses against the skin of the patient when the flat member is attached thereto, and the second surface comprises an interface surface which is shaped to receive the noninvasive optical measurement system.